Internally cooled mandrel



Dec. 30, 1958 H. E. HONKALA ETAL 2,866,545

INTERNALLY COOLED MANDREL Filed May 7, 1956 1 I 1 I I I l I I I I I 1:

36 48 G 4 INVENTORS HAROLD E NNNNNNNNNNNNNNNN M United States Patent INTERNALLY 'COOLED MAN DREL Application May 7, 1956, Serial No. 583,236

Claims. (Cl. 207-46) The present invention relates to an internally cooled mandrel, and more particularly to an internally cooled mandrel for use in tube extrusion provided with pressure relief means.

It is an object of the present invention to provide a mandrel for use in extruding tube having a coolant pas- Sage therein including means normally closing the outer end of the passage and means responsive to elongation of the mandrel for opening the valve to relieve pressure in the event of failure of the mandrel.

More specifically, it is an object of the present invention to provide an internally cooled mandrel for use in tube extrusion having an elongated passage extending longitudinally thereof and terminating in a reduced opening at the outer end of the mandrel, a coolant tube extending longitudinally of the passage, a plug in said opening, and means connecting the outer end of said tube and said plug operable to withdraw the plug from the opening upon elongation of the mandrel.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, wherein:

Figure l is a fragmentary sectional view showing the relationship of die, mandrel, and associated structure employed in extruding tubing.

Figure 2 is an enlarged longitudinal sectional view showing the outer end of the mandrel in operating condition.

Figure 3 is a sectional view similar to Figure 2 showing the relationship of parts just prior to failure of the mandrel.

Figure 4 is a fragmentary axial sectional view of a modified form of pressure relief construction.

Referring now to the drawings, there is illustrated a die having a circular opening 12 therethrough in which is positioned the outer end of a mandrel 14. An annular pressure head 16 is received within the circular opening 18 of a container 20 and is engaged by the outer end of a tubular stem 22. Received between the die 10 and the pressure head 16 is a billet B of the material of which the tube is formed. The billet B is heated to the appropriate temperature, is placed within the container and is pierced by forward movement of the mandrel 14 which is accomplished by moving the mandrel holder 24 forwardly by suitable means such for example as a hydraulic cylinder.

After the billet B has been pierced the stem 22 is advanced to force the pressure head to the left as seen in Figure 1, and the material of the billet B is extruded through the annular space between the opening 12 in the die and the outer surface of the mandrel 14. Since the billet B is heated and since heavy frictional resistance is encountered, there is a tendency for the parts and particularly the mandrel, to become very hot. As disclosed in prior Patent 2,698,683, cooling means have been provided for the mandrel and these means comprise 2,866,545 Patented Dec. 30, .1958

a longitudinally extending passage 26 in which is provided a conduit or spray tube 28. The spray tube has distributed longitudinally thereof ports 30. Liquid coolant such as Water, is" introduced into the inner end of the spray tube 28 and escapes into the annular space between the spray tube and the passage 26. This serves to carry away a substantial amount of heat generated during the extrusion process and permits re-use of the mandrel to pierce another billet as soon as the preceding billet has been completely extruded.

The extrusion operation necessarily involves substantial tensile stresses on the mandrel 14 due to the drag of the metal of billet B as it is extruded through the die 10, and thus the mandrel occasionally fails in use.

When the mandrel 14 breaks, the broken end is frictionally retained in the previously extruded portions of the tube which is travelling at a faster rate of speed than the metal surrounding the end of the broken mandrel. Thus, when the mandrel breaks, solid rod is extruded behind the previously extruded tube portions, completely sealing the rear end of the water passage 26. Water may thus be sealed in the partially extruded tube since the outer portion of the mandrel has separated from the inner portion and is frictionally retained in the interior of the partially extruded tube. Thus water, converted to steam by reason of the intense heat developed by the operations, results in dangerously high pressures Within the sealed tube portions. As a result of the pressure, the extruded tube portion may rupture or the broken off end of the mandrel may be propelled from the partial-1y extruded tube at high velocity, causing danger of personal injury or property damage.

The failure of the mandrel is normally in tension and results in separation of the mandrel. This failure in its preliminary stage results in necking down of the mandrel as illustrated at 32 in Figure 3, before actual rupture takes place, as indicated at 34. Accordingly, as the preliminary phase of mandrel failure, there is an elongation of the mandrel.

In accordance with the present invention this elongation of the mandrel which precedes rupture thereof is employed to control operation of pressure relief means. As best seen in Figures 2 and 3, the outer end of the pas sage 26 terminates in a reduced port or opening 36. The outer end of the spray tube 28 is closed by a cup 38 which is apertured to receive the stem 40 of a plug valve 42, the valve having an annular shoulder 44 intermediate its ends. The inner end of the stem is threaded for the reception of a nut 46. Under normal operating conditions the plug valve 42 is located within the openin 36 and operates as an effective closure for the opening. However, during operation if the mandrel 14 starts to fail, it will neck down as indicated at 32 and prior to actual rupture will elongate to an extent which withdraws the valve portion 42 from the opening 36. This provides a relief passage which prevents the building up of steam pressure and avoids the dilficulties previously mentioned.

Instead of employing the metal plug valve 42 as best seen in Figures 2 and 3, it is possible to employ a valve of the type shown at 48 in Figure 4. The valve 48 may be formed of rubber or similar material and is adapted to overlie the opening 36 rather than to enter into it as is the case of the valve plug 42. This valve is thus yieldable and like valve 42 will maintain the opening closed during slight relative elongation of the mandrel.

The drawings and the foregoing specification constitute a description of the improved internally cooled mandrel in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What we claim as our invention is:

1. An internally cooled mandrel for use in tube extrusion and subjected in use to tensile stresses and having a longitudinally extending passage terminating in an opening at the outer end thereof, means for supplying cooling liquid to said passage, a valve normally closing said opening, and means in said passage responsive to elongation of said mandrel for opening said valve.

2. An internally cooled mandrel for use in tube extrusion and subjected in use to tensile stresses and hav ing a longitudinally extending passage terminating in an opening at the outer end thereof, means for supplying cooling liquid to said passage, an elongated support memer in said passage having its inner end fixed and its outer end free for relative movement in the end of said.

passage adjacent the outer end of said mandrel, a valve normally closing said opening, said valve being carried by the free end of said member, whereby upon elongation of said mandrel under the tensile stress applied thereto, said valve opens to provide for escape of cooling liquid.

3. An internally cooled mandrel for use in tube extrusion and subjected in use to tensile stresses and having a longitudinally extending passage terminating in an opening at the outer end thereof, means for supplying cooling liquid to said passage, comprising an elongated conduit extending longitudinally of said passage having its inner end fixed and its outer end free for relative movement in the end of said passage adjacent the free end of said mandrel, said conduit having ports for the escape of cooling liquid nto said passage, a valve normally closing said opening, said valve being carried by the free end of said conduit, whereupon upon elongation of said mandrel under the tensile stress applied thereo, said valve opens to provide for escape of cooling liquid.

References Cited in the file of this patent UNITED STATES PATENTS 1,374,369 Earl Apr. 12, 1921 1,989,948 Singer Feb. 5, 1935 2,385,574 Hyprath Sept. 25, 1945 2,698,683 Martin et al. Jan. 4, 1955 

